Nagashima-type palmoplantar keratoderma (NPPK) is an autosomal recessive genodermatosis caused by loss-of-function variants in SERPINB7 and is the most prevalent form of inherited palmoplantar keratodermas among Asians. However, there is currently no effective therapy for NPPK because its pathogenesis remains unclear. In this study, Serpinb7-/- mice were generated and spontaneously developed a disrupted skin barrier, which was further exacerbated by acetone-ether-water treatment. The skin of these Serpinb7-/- mice showed weakened cytoskeletal proteins. Additionally, SERPINB7 deficiency consistently led to decreased epidermal differentiation in a three-dimensional human epidermal model. We also demonstrated that SERPINB7 was an inhibitory serpin that mainly inhibited the protease legumain. SERPINB7 bound directly with legumain and inhibited legumain activity both in vitro and in vivo. Furthermore, we found that SERPINB7 inhibited legumain in a \'protease-substrate\' manner and identified the cleavage sites of SERPINB7 as Asn71 and Asn343. Overall, we found that SERPINB7 showed the nature of a cysteine protease inhibitor, and identified legumain as a key target protease of SERPINB7. Loss of SERPINB7 function led to overactivation of legumain, which might disrupt cytoskeletal proteins, contributing to the impaired skin barrier in NPPK. These findings may lead to the development of therapeutic strategies for NPPK.

Mutilating palmoplantar keratoderma (PPK) is a heterogeneous genetic disease that poses enormous challenges to clinical diagnosis and genetic counselling. Lanosterol synthase (LSS) gene encodes LSS involved in the biosynthesis pathway of cholesterol. Biallelic mutations in LSS were found to be related to diseases such as cataracts, hypotrichosis and palmoplantar keratoderma-congenital alopecia syndrome. The aim of this study was to investigate the contribution of the LSS mutation to mutilating PPK in a Chinese patient. The clinical and molecular characteristics of the patient were evaluated. A 38-year-old male patient with mutilating PPK was recruited in this study. We identified biallelic variants in the LSS gene (c.683C > T, p.Thr228Ile and c.779G > A, p.Arg260His). Immunoblotting revealed that the Arg260His mutant showed a significantly reduced expression level while Thr228Ile showed an expression level similar to that of the wild type. Thin layer chromatography revealed that mutant Thr228Ile retained partial enzymatic activity and mutant Arg260His did not show any catalytic activity. Our findings show the correlation between LSS mutations and mutilating PPK.

Dominant variants in the gap junction beta-2 (GJB2) gene may lead to various degrees of syndromic hearing loss (SHL) which is manifest as sensorineural hearing impairment and hyperproliferative epidermal disorders, including palmoplantar keratoderma with deafness (PPKDFN). So far, only a few GJB2 dominant variants causing PPKDFN have been discovered. Through the whole-exome sequencing (WES), a Chinese female patient with severe palmoplantar hyperkeratosis and delayed-onset hearing loss has been identified. She had a novel heterozygous variant, c.224G>C (p.R75P), in the GJB2 gene, which was unreported previously. The proband\'s mother who had a mild phenotype was suggested the possibility of mosaicism by WES (∼120×), and the ultra-deep targeted sequencing (∼20,000×) was used for detecting low-level mosaic variants which provided accurate recurrence-risk estimates and genetic counseling. In addition, the analysis of protein structure indicated that the structural stability and permeability of the connexin 26 (Cx26) gap junction channel may be disrupted by the p.R75P variant. Through retrospective analysis, it is detected that the junction of extracellular region-1 (EC1) and transmembrane region-2 (TM2) is a variant hotspot for PPKDFN, such as p.R75. Our report reflects the important and effective diagnostic role of WES in PPKDFN and low-level mosaicism, expands the spectrum of the GJB2 variant, and furthermore provides strong proof about the relevance between the p.R75P variant in GJB2 and PPKDFN.

Papillon-Lefevre syndrome (PLS) (OMIM: 245000) is a rare autosomal recessive disorder characterized by palmoplantar hyperkeratosis and early onset periodontitis, resulting in the premature loss of the deciduous and permanent teeth. PLS is caused by mutations in the cathepsin C (CTSC) gene (OMIM: 602365), which has been mapped to chromosome 11q14-q21. Genetic analysis can help early and rapid diagnosis of PLS. Here we report on a Chinese PLS pedigree with two affected siblings. We have identified two novel compound heterozygous mutations c.763T>C (p.C255R) and c.1015C>A (p.R339S) in the CTSC gene. The two mutations expand the spectrum of CTSC mutations in PLS.

Severe dermatitis, multiple allergies and metabolic wasting (SAM) syndrome is a recently recognized syndrome caused by mutations in the desmoglein 1 (DSG1) and desmoplakin (DSP) genes. Only two cases of SAM-DSP have been reported. We report on a 2-year-old girl presenting with pustular lakes within areas of erythema and large accumulations of intraepidermal neutrophils, which initially led to our misdiagnosis of generalized pustular psoriasis. No mutation was found in either the IL36RN or CARD14 genes by Sanger sequencing. The distinctive manifestations of erythroderma with severe itching, hypotrichosis, enamel defects, onychodystrophy, palmoplantar keratoderma and the crucial result of de novo missense mutation in exon 14 of the DSP gene (c.1828T>C, p.S610P) discovered by next-generation sequencing finally confirmed the diagnosis of SAM syndrome. The eruptions significantly improved after a 4-week treatment with oral acitretin and topical pimecrolimus. Oral gabapentin was prescribed simultaneously for 4 months, relieving her skin pruritus and suggesting that early treatment with pimecrolimus, acitretin and gabapentin for SAM-DSP syndrome is effective. It may even inhibit multiple allergies induced by skin barrier injury. In this work we also review the clinical features, differential diagnoses and pathological manifestations of SAM-DSP syndrome.

BACKGROUND: Pachyonychia congenita (PC), a rare autosomal dominant disorder, is featured by significant hypertrophic nail, palmoplantar keratoderma, and plantar pain. It is caused by the mutation of KRT6A, KRT6B, KRT6C, KRT16, or KRT17.
OBJECTIVE: To identify the gene mutation caused the PC in a Chinese family.
METHODS: Genomic DNA was extracted from peripheral blood samples of five patients and six healthy individuals. Genomic DNA of three patients was sequenced by whole-exome sequencing (WES). Then, exons 6 of KRT16 of all samples were amplified by polymerase chain reaction (PCR), and PCR products were sequenced to identify potential mutations.
RESULTS: We identified the proline substitution mutation p.Leu421Pro (c.1262T>C) in the 2B domain of K16 that is associated with PC in a Chinese family. The same mutation was not found in the six healthy individuals of the family.
CONCLUSIONS: The mutation found in this study is the first report in China. So far, 25 mutations in KRT16 have been reportedly associated with PC. Twenty-one mutations are located on exon 1, and four mutations on exon 6.

OBJECTIVE: Mutations in the GJB2 gene encoding connexin 26 (Cx26) are major causes of hereditary deafness. This study aimed to characterize the mutation profiles of the GJB2 gene in a Chinese family with sensorineural hearing loss.
METHODS: A Chinese family that included three individuals with sensorineural hearing loss and palmoplantar keratoderma underwent complete physical examinations, audiological examinations including pure tone audiometry and auditory brainstem response, skin pathological examination, and temporal CT scans. The entire coding region of GJB2, GJB3, GJB6, and the coding exons (exon7+8 and 19) of SLC26A4, mitochondrial 12SrRNA, and tRNA Ser (UCN) were sequenced. Structural analysis was performed to detect the effects of mutation on the tertiary structure of Cx26.
RESULTS: A dominant GJB2 mutation, c.224G>A (p.Arg75Gln, p.R75Q), was detected in the family. No other mutation was identified in GJB2, GJB3, GJB6, or the coding exons (exon7+8 and 19) of SLC26A4, mitochondrial 12SrRNA, and tRNA Ser (UCN). Structural analysis revealed that the p.R75Q mutation likely affects the structural stability and permeation properties of the Cx26 gap junction channel.
CONCLUSIONS: Our findings provide further evidence of a correlation between the p.R75Q mutation in Cx26 and a syndromic hearing impairment with palmoplantar keratoderma.